This invention relates to golf balls. More particularly it relates to solid core golf balls having an improved coefficient of restitution.
Unitary golf balls, also known as two-piece solid core golf balls, are widely accepted in the golfing industry as being highly durable. This is attributed to the presence of the solid core and a unitary or multi-ply highly cut resistant cover. As with all golf balls, the industry continually endeavors to find ways to improve the distance a golf ball will travel when hit by a golf club. This improvement activity is limited, however, by the rules of the United State Golf Association which state that the intitial velocity of a golf ball cannot exceed 250 .+-.5 feet/second.
It is recognized that the distance a golf ball will travel when struck by a golf club is a function of many factors such as angle of trajectory, clubhead speed and coefficient of restitution. Of these three factors, the golf ball manufacturers have control over the latter, i.e. coefficient of restitution ("COR") which is the ratio of the outgoing velocity to the incoming velocity of a golf ball as expressed as a decimal. Such control is exercised by the golf ball manufacturers through the methods and materials employed to produce golf balls.
As is known in the industry, the COR of a golf ball is a function of both the core and the cover. The greater the contribution of the core, the lesser need be the contribution of the cover. As the core comprises the major portion of any golf ball, COR improvements have primarily been achieved by modification of the core; however, said modification must not exessively effect the compressibility of the golf ball which is a prerequisite to playability of the golf ball.
There are a number of golf balls disclosed in the prior art which demonstrate a tradeoff between high COR and compressibility. For example, U.S. Pat. No. 4,726,590 (Molitor) discloses one piece golf ball cores which exhibit a maximum COR of 0.815; however, said golf balls also exhibit decreasing compressibility with increasing COR.
U.S. Pat. No. 4,838,556 (Sullivan) discloses a golf ball with a solid core wherein the COR is increased due to the presence of a special dispersing agent. While the maximum COR disclosed was 0.816, this occurred at the lowest compressibility.
U.S. Pat. No. 4,852,884 (Sullivan) discloses a solid core for a golf ball which is formed using a metal carbonate accelerator. The highest COR achieved in this Patent, while still maintaining a satisfactory compressibility, was 0.807. Similarly, U.S. Pat. No. 4,844,471 (Terrence) forms a solid core using a dialkyl tin fatty acid. Employing this addition, the highest COR attained, while maintaining a satisfactory compressibility, was 0.809.
While not directly addessing the problem of increasing the COR while retaining sufficient compressibility, U.S. Pat. No. 4,546,980 (Gendreau et al) discloses a solid core which contains two or more free radical initiators, at least two of which exhibit a different reactivity during the curing process. Golf balls made under the disclosure of this invention are claimed to have an initial velocity of at least 0.5 feet/second higher than the same golf ball made with only one initiator.
Accordingly, it is an object of the present invention to provide a core for a golf ball which provides a high COR and good compressibility.
It is a further object of the present invention to provide golf balls which exhibit superior playability while maintaining a high COR.